Processes of chemical nickel plating of nonmetallic bodies



Patented Sept. 28, 1954 PROCESSES OF CHEMICAL NICKEL PLATING OF NONMETALLIO BODIES William J. Crehan, Hinsdale, Ill., assignor to General American Transportation Corporation, Chicago, 111., a corporation of New York No Drawing. Application April 1, 1952, Serial No. 279,945

8 Claims.

The present invention relates to processes of chemical nickel plating of non-metallic bodies, and constitutes an improvement over that disclosed and claimed in the copending application of Gregoire Gutzeit, William J. Crehan and Abraham Krieg, Serial No. 230,352, filed June '7, 1951.

In this Gutzeit, Crehan and Krieg application, there is disclosed an improved process of chemi cally nickel plating a non-metallic body formed of such materials as plastics, hard rubber, wood, ceramics, and the like, by freshening the surface of the body (removing the outer skin thereof), then contaminating the freshened surface of the body with a catalytic material, and then contacting the body with a chemical nickel plating bath. In accordance with that process, the initial surface of the body is freshened in order to remove the polarized outer skin thereof by sanding, blasting, brushing, grinding, buffing, abrading, tumbling, chemical etching, etc.; and the catalytic material with which the freshened surface of the body is contaminated essentially comprises one or more elements selected from the group consisting of copper, silicon, gold, beryllium, boron, germanium, aluminum, thallium, silicon, carbon, vanadium, molybdenum, tungsten, chromium, selenium, tellurium, titanium, iron, cobalt, nickel, palladium and platinum. Finally, in that process, the prepared body is immersed for a suitable time interval in a chemical nickel plating bath of the nickel cation-hypophosphite anion type. In the preparation of the body, the freshened surface thereof is contaminated with a sufiicient amount of the catalytic material so as to form thereon firmly anchored growth nuclei, it being unnecessary to achieve a complete coverage of the freshened surface of the body with the growth nuclei since the nickel plating spreads for a certain distance from each growth nucleus in the two dimensions along the surface of the material as it builds up in the third dimension upon the growth nucleus, the freshened surface areas between the growth nuclei accommodating the intimate bonding of the nickel plating in these areas; whereby a complete and homogeneous coating of nickel upon the surface of the body is obtained.

While the process disclosed in this Gutzeit, Crehan and Krieg application is entirely satisfactory in the nickel plating of a non-metallic body, it is dependent upon the careful preparation of the surface of the body, and particularly upon the substantially uniform contamination of the freshened surface thereof with the catalytic material to provide a substantially uniform distribution of the growth nuclei firmly anchored thereon,

2 whereby the process is more expensive to carry out commercially than is desirable.

Accordingly, it is the general object of the present invention to provide an improved process of chemical nickel plating of non-metallic bodies that is simple and economical to carry out commercially.

Another object of the invention is to provide a process of producing an intimately bonded layer of nickel upon a non-metallic body formed essentially of such materials as synthetic plastics, hard rubber, wood, quartz, glass, ceramics, or the like, that involves exposing a fresh surface of the body, applying a palladium salt to the fresh surface of the body, chemically reducing the palladium salt applied to the fresh surface of the body to metallic palladium intimately bonded thereto, and then chemically depositing nickel upon the metallic palladium and upon the fresh surface of the body.

A further object of the invention is to provide a process of the character described, wherein the palladium salt is applied to the fresh surface of the non-metallic body by immersing the body in a first aqueous solution of the palladium salt, the palladium salt applied to the fresh surface of the body is reduced to metallic palladium by immersing the body in a second aqueous solution of a reducing agent, and the nickel is chemically deposited upon the metallic palladium and upon the fresh surface of the body by immersing the body in an aqueous chemical nickel plating bath of the nickel cation-hypophosphite anion type.

A still further object of the invention is to provide a process of the character described, wherein the concentration of the palladium salt in the aqueous solution mentioned is quite low, so that after the palladium salt is applied to the fresh surface of the body and then chemically reduced to metallic palladium, the metallic palladium is applied uniformly to the fresh surface of the body, although not necessarily continuously, and adequately to provide securely anchored growth nuclei thereon in order that subsequently the nickel may be chemically deposited upon the metallic palladium and upon the fresh surface of the body to provide a continuous layer of the nickel of the required thickness upon the body.

In accordance with the process of the present invention, the non-metallic body formed essentially of such materials as synthetic plastics, hard rubber, wood, quartz, glass, ceramics, or the like, is first prepared by freshening the surface thereof upon which the nickel is to be ultimately deposited employing any conventional step, such as,

sanding, blasting, brushing, grinding, buffing, abrading, tumbling, chemical etching, etc., so as to remove the outer skin thereof in order to eliminate any polarization of the surface of the body. For instance, liquid honing with Vapor Blast equipment using Novacuiite 325 or 1250 mesh abrasive or dry blasting with 325 mesh emery powder is very effective to prepare or freshen the surface of the body, particularly when it is formed of a synthetic plastic material, such as Bakelite, methacrylate, polystyrene, etc. After the surface of the non-metallic body is thus freshened, the body is immersed for a short time interval in a first aqueous solution containing a soluble salt of palladium, such as, the chloride, nitrate, bromide, or sulfate; and is then removed therefrom and rinsed with water, or the like. For instance, merely by dipping the pre" pared body into the first solution and. then rinsing with water, a suitable quantity of the palladium salt is applied to the fresh surface and remains thereon for the present purposes. It is particularly noted that the concentration of the palladium salt in the first solution is exceedingly low; for example, employing a first solution essentially comprising only water and palladium chloride, it was discovered that the concentration of the palladium chloride in the water is effective above 35 parts of palladium chloride to each 1,000,000 part of water, by weight.

Thereafter, the non-metallic body is immersed for a short time interval in a second aqueous solution containing a soluble chemical reducing agent, such as, hypophosphorous acid, hydrazine hydrochloride, hydroquinone, etc.; and is then removed therefrom and rinsed with water, or the like. For instance, merely by dipping the prepared body into the second solution and then rinsing with water, a suitable quantity of the palladium salt applied to the fresh surface of the body is chemically reduced to metallic palladium to form substantially uniformly distributed growth nuclei securely anchored thereto. It is particularly noted that the metallic palladium nuclei thus securely anchored to the fresh surface of the body need not be continuous or provide a monatomic layer since the nickel subsequently deposited upon each metallic palladium nucleus will spread therefrom in the two directions along the fresh surface of the body as it builds up in the third dimension upon the nucleus, thereby obtaining ultimately a complete and homogeneous coating of nickel upon the surface of the body. The fresh surface areas of the body between the growth nuclei permit ready spreading of the nickel deposit by virtue of the elimination of the polarization thereof. For example, employing the second solution essentially comprising only water and a soluble hypophosphite, i. e., about 0.225 mole/liter of hypophosphite anion derived from sodium hypophosphite, the palladium chloride applied to the fresh surface of the non-metallic body is quickly and completely reduced to metallic palladium.

Finally, the non-metallic body is then immersed for the required time interval in a chemical nickel plating bath of the nickel cationhypophosphite anion type, the time interval required being dependent upon the thickness of the nickel plating that is desired upon the surface of the body; and is then removed therefrom and rinsed with water, or the like. For instance, by immersing the prepared body into the chemical nickel plating bath and then rinsing with water, an intimately bonded layer of nickel (containing some phosphorus) is deposited upon the surface thereof. The temperature of the bath is preferably slightly below the boiling point thereof, about 98 C. or 99 C.

While there are several known chemical nickel plating baths of the nickel cation-hypophosphite anion type, the baths respectively disclosed in the copending application of Gregoire Gutzeit and Abraham Krieg, Serial No. 194,656, filed November 3,1950, now Patent No. 2,658,341, granted November 10, 1953, and in the copending application of Gregoire Gutzeit and Ernest J. Ramirez, Serial No. 204,424, filed January 4, 1951, now Patent No. 2,658,842, granted November 10, 1953, are specifically recommended.

Thebath disclosed in the Gutzeit and Krieg application essentially comprises an aqueous acid solution containing nickel cations, hypophosphite anions and a buffer in the form of a soluble salt of monocarboxylic acid; the initial pH of the bath being within the approximate range 4.5 to 5.6. In this bath, the ratio between nickel cations and hypophosphite anions, expressed in molar concentrations, is within the range 0.25 to 0.60; the absolute concentration of hypophosphite anions, expressed in mole/liter, is within the range 0.15 to 0.35; the absolute concentration of the buffer is equivalent to two carboxyl groups for every nickel cation that can be deposited, for instance, in the case of sodium acetate, at least 0.120 mole/liter of acetate anion. The bath may be formed by dissolving in a water solution of hydrochloric acid, nickel chloride, sodium hypophosphite and sodium acetate, the pH of the bath being adjusted with a weak alkali, such as sodium bicarbonate.

The bath disclosed in the Gutzeit and Ramirez application essentially comprises an aqueous acid solution containing nickel cations, hypophosphite anions and an exaltant in the form of a soluble salt of a simple short chain aliphatic dicarboxylic acid, the initial pH of the bath being within the approximate range 4.3 to 6.8. In this bath, the ratio between nickel cations and hypophosphite anions, expressed in molar concentrations, is within the range 0.25 to 0.60; the absolute concentration of hypophosphite anions, expressed in mole/liter is within the range 0.15 to 0.20; the absolute concentration of the exaltant is equivalent to two carlboxyl groups for every nickel cation that can be deposited, for instance in the case of sodium succinate, at least 0.05 mole/liter of succinate anion. The bath may be formed by dissolving in a water solution of hydrochloric acid, nickel chloride, sodium hypophosphite and sodium succinate, the pH of the bath being adjusted with a weak alkali, such as, sodium bicarbonate.

In carrying out the present process, it is very important that the palladium salt applied to the fresh surface of the non-metallic body be chemically reduced to metallic palladium to provide the growth nuclei securely anchored to the surface of the body before the body is immersed in the chemical nickel plating bath, as otherwise the palladium salt will become diffused throughout the chemical nickel lating bath incident to the immersion of the body, whereby black precipitate will quickly form in the chemical nickel plating bath. Not only is the formation of black precipitate in the chemical nickel plating bath objectionable, as it comprises a random reduction of the nickel cations therein, as contrasted with catalytic reduction of nickel cations therein upon the surface of the body undergoing the plating, but the chemical nickel plating bath is quickly depleted once the formation of black precipitate therein is initiated, since the reaction producing the black precipitate in the chemical nickel plating bath is autocatalytic. Furthermore, when black precipitate begins to form in the chemical nickel plating bath, further deposition of nickel upon the surface of the body is quickly arrested and the deposit of metallic nickel thereon is rendered rough or at least the normal brightness thereof is seriously impaired. However, when the alladium salt applied to the surface of the body by dipping in the first solution is chemically reduced to metallic palladium by dipping in the second solution, preceding the immersion of the body in the chemical nickel plating bath, the palladium is immobilized upon the surface of the body, so that subsequently there is no tendency for the palladium cations to diffuse through the chemical nickel plating bath and initiate the production of the objectionable black precipitate, as explained above.

In the first solution, a concentration of palladium chloride in excess of about 35 parts per 1,000,000 parts of water, by weight, merely brings about the application to the surface of the nonmetallic body of additional growth nuclei, as a consequence of the chemical reduction thereof in the second solution, whereby the metallic palladium applied to the fresh surface of the body tends toward a monatomic layer, so that the initiation of the nickel plating thereon in the chemical nickel plating bath is accelerated. However, since palladium salts are rather expensive and initiation of the nickel plating takes place, as previously described, when the concentraticn of the nickel chloride in the first solution is at least about 35 parts per 1,000,000 parts of water, by weight, it is uneconomical substantially to increase the concentration of the palladium salt in the first solution materially beyond that noted.

In carrying out the process of the present invention, the initiation of chemical nickel plating upon the growth nuclei and upon the fresh surface of the body is substantially instantaneous when the body is immersed in the chemcal nickel plating bath, and the thickness of the nickel plating (containing some phosphorus) that may be built up thereon is dependent only upon the immersion time interval. For example, in a matter of only several hours a nickel coating of several mils in thickness may be deposited upon a non-metallic body, which coating is hard,

smooth and bright, intimately bonded to the surface of the body, and exhibits great resistance to oxidation and corrosion.

From the foregoing, it is apparent that an improved process has been provided for the plating with nickel of non-metallic bodies formed of such materials as synthetic plastics, hard rubber, wood, glass, ceramics, etc., that involves the preliminary activation or preparation of the surface of the bodies employing the method of the present invention so as to provide thereon firmly anchored metallic palladium growth nuclei and nonpolarized areas therebetween accommodating the initiation of the chemical nickel plating thereupon incident to the immersion of the bodies in the chemical nickel plating bath of the nickel cation-hypophosphite anion type. It will be understood that the invention is not limited except as defined by the appended claims.

What is claimed is:

1. The process of producing an intimately bonded and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises eXp-osing a fresh non-polarized surface of said body, then contacting said body with a first aqueous solution of a palladium salt, then contacting said body with a second aqueous solution of a reducing agent in order to effect the chemical reduction of said palladium salt to metallic pal lad ium so that dispersed minute metallic palladium particles are secured to the fresh nonpolarized surface of said body, and then contacting said body with a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a sufficient time interval to cause initial nickel plating upon said particles and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh nonpolarized surface of said body.

2. The process of producing an intimately bonded and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh non-polarized surface of said body, then contacting said body with a first aqueous solution of a palladium salt, then rinsing said body, then contacting said body with a second aqueous solution of a reducing agent in order to effect the chemical reduction of said palladium salt to metallic palladium so that dispersed minute metallic palladium particles are secured to the fresh non-polarized surface of said body, then rinsing said body, and then contacting said body with a bath consisting essentially of an aqueous solution of a nickel salt and a hypo phosphite during a sufficient time interval to cause initial nickel plating upon said particles and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh nonpolarized surface of said body.

3. The process set forth in claim 1, wherein said palladium salt is palladium chloride.

4. The process set forth in claim 1, wherein said first aqueous solution is of palladium chloride containing by weight at least 35 parts of palladium chloride to 1,000,000 parts of water.

5. The process set forth in claim 1, wherein said reducing agent is a hypophosphite.

6. The process set forth in claim 1, wherein said palladium salt is palladium chloride and said reducing agent is a hypophosphite.

7. The process of producing an intimately bonded and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh non-polarized surface of said body, applying a palladium salt to the fresh non-polarized surface of said body, then chemically reducing said palladium salt applied to the fresh non-polarized surface of said body to metallic palladium so that dispersed minute metallic palladium particles are secured to the fresh non-polarized surface of said body, and then contacting said body with a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a sufiicient time interval to cause initial nickel plating upon said particles and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh non-polarized surface of said body.

8. The process of producing an intimately bonded and continuous layer of nickel upon the surface of a solid non-metallic body, which comprises exposing a fresh non-polarized surface of said body, applying a palladium salt to the fresh non-polarized surface of said body by immersing said body in a first aqueous solution of said palladium salt, then chemically reducing said palladium salt applied to the fresh non-polarized surface of said body to metallic palladium by immersing said body in a second aqueous solution of a reducing agent so that dispersed minute metallic palladium particles are intimately bonded to the fresh non-polarized surface of said body, and then immersing said body in a bath consisting essentially of an aqueous solution of a nickel salt and a hypophosphite during a sufiicient time interval to cause initial nickel plating upon said particles and subsequent growth of the nickel plating into a continuous nickel layer upon the fresh nonpolarized surface of said body.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,430,581 Pessel Nov. 11, 1947 10 2,532,283 Brenner Dec. 5, 1950 

1. THE PROCESS OF PRODUCING AN INTIMATELY BONDED AND CONTINUOUS LAYER OF NICKEL UPON THE SURFACE OF A SOLID NON-METALLIC BODY, WHICH COMPRISES EXPOSING A FRESH NON-POLARIZED SURFACE OF SAID BODY, THEN CONTACTING SAID BODY WITH A FIRST AQUEOUS SOLUTION OF A PALLADIUM SALT, THEN CONTACTING SAID BODY WITH A SECOND AQUEOUS SOLUTION OF A REDUCING AGENT IN ORDER TO EFFECT THE CHEMICAL REDUCTION OF SAID PALLADIUM SALT TO METALLIC PALLADIUM SO THAT DISPERSED MINUTE METALLIC PALLADIUM PARTICLES ARE SECURED TO THE FRESH NONPOLARIZED SURFACE OF SAID BODY, AND THEN CONTACTING SAID BODY WITH A BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF A NICKEL SALT AND A HYPOPHOPHITE DURING A SUFFICIENT TIME INTERVAL TO CAUSE INITIAL NICKEL PLATING UPON SAID PARTICLES AND SUBSEQUENT GROWTH OF THE NICKEL PLATING INTO A CONTINUOUS NICKEL LAYER UPON THE FRESH NONPOLARIZED SURFACE OF SAID BODY. 